|By Joseph Sipalan

KUALA LUMPUR (Reuters) - Malaysia's veteran former leader Mahathir Mohamad campaigned against his old party over the weekend, seeking to turn voters against scandal-tainted Prime Minister Najib Razak in two by-elections being fought next week.

Mahathir, who led the country for 22 years until his retirement in 2003, quit the United Malays National Organisation (UMNO) earlier this year in disgust over Najib's grip on the party despite allegations of massive corruption.

The feisty 90-year-old has teamed up with old foes in the Pakatan Harapan opposition alliance to remove Najib, his one-time protege.

"If the people want to see this country being robbed by the PM, who has now passed a law that makes him stronger than even the Agong (King)... If that's what the people want, they'll get what they deserve," Mahathir told a news conference while campaigning on Saturday.

Najib, who denies any wrongdoing, has seen his popularity sink to all time lows because of a multi-billion dollar graft scandal at the 1Malaysia Development Bhd (1MDB) state fund and reports that around $1 billion were deposited in his personal bank account.

The multi-ethnic Barisan Nasional coalition led by UMNO has lost support among the Southeast Asian nation's ethnic Chinese and Indian minorities because the controversy, leaving the embattled premier desperately trying to shore up his Muslim Malay votebank.

Last month, UMNO convinced parliament to allow members to debate a bill submitted by the Pan-Malaysian Islamic Party (PAS) - which has stayed outside the anti-Najib alliance - for the introduction of hudud, the Islamic penal code that sets punishments like amputation and stoning.

The constituencies being contested on June 18, midway through the Muslim fasting month of Ramadan, are largely Malay, and the only runner that the anti-Najib alliance has in the race is a new moderate Islamist party that splintered from PAS.

The by-elections at Sungai Besar and Kuala Kangsar will show how well support for Najib is holding up, with an eye to a national election due in 2018.

Mahathir on Saturday carried his anti-Najib message to Sungai Besar, a coastal town amid the paddy fields, coconut groves and palm oil plantations on the western side of the Malaysian Peninsula.

He called on voters to rally behind the candidate from the newly-formed National Trust Party, known as Amanah.

"It doesn't matter what party, these are parties for the people against Najib because he has committed a lot of corruption, including misappropriating up to 50 billion ringgit ($12 billion) that cannot be explained," Mahathir said, referring to the troubles at 1MDB, whose advisory board had been chaired by Najib until recently.

HUDUD GAMBIT

Najib has strengthened his grip over UMNO by purging dissidents including a deputy prime minister and, worryingly for non-Muslim Malaysians, he has also built bridges with PAS, whose Islamist hardliners make up the second-largest Malay party.

Oh Ei Sun, senior fellow at the S. Rajaratnam School of International Studies, said UMNO and PAS had insufficient votes to force the hudud bill through parliament, and saw the issue as a ploy to distract Malay voters away from 1MDB.

Some analysts suspect Najib of testing the ground for working with PAS to secure a victory at the next general election.

"UMNO is trying to use the Islamic card to build a relationship with PAS," Professor James Chin, director at the University of Tasmania's Asia Institute.